Some Git internals

#1

Post by ingve » Fri, Dec 25, 2020, 6:19 PM UTC

Re: Some Git internals

#2

Post by Waterluvian » Fri, Dec 25, 2020, 9:34 PM UTC

This was really really educational. Git internals seem rather simple.

Does anyone have a really good visual explanation of what's being done to the tree and such when commits and merges and rebases are done? I still don't quite grok it intimately enough.

Re: Some Git internals

#3

Post by rustybolt » Fri, Dec 25, 2020, 9:57 PM UTC

Waterluvian wrote: post #2

This was really really educational. Git internals seem rather simple. Does anyone have a really good visual explanation of what's being done to the tree and such when commits and merges and rebases are done? I still don't quite grok it intimately enough.

learngitbranching.js.org is quite good

Re: Some Git internals

#4

Post by divbzero » Fri, Dec 25, 2020, 10:00 PM UTC

Waterluvian wrote: post #2

This was really really educational. Git internals seem rather simple. Does anyone have a really good visual explanation of what's being done to the tree and such when commits and merges and rebases are done? I still don't quite grok it intimately enough.

The Git Internals section of the Pro Git book covers commits [1] and branches [2] well though it doesn’t go into details about merges and rebases.

[1]: https://git-scm.com/book/en/v2/Git-Internals-Git-Objects

[2]: https://git-scm.com/book/en/v2/Git-Internals-Git-References

Re: Some Git internals

#5

Post by aequitas » Fri, Dec 25, 2020, 10:26 PM UTC

Waterluvian wrote: post #2

This was really really educational. Git internals seem rather simple. Does anyone have a really good visual explanation of what's being done to the tree and such when commits and merges and rebases are done? I still don't quite grok it intimately enough.

Ungit[0] shows what will happen to the tree before you execute a merge or rebase. It really helped me get a hang of Git.

[0] https://github.com/FredrikNoren/ungit

Re: Some Git internals

#6

Post by ufo » Fri, Dec 25, 2020, 10:36 PM UTC

A dumb question: if I make a commit changing just a single line in a large file, does this create a completely new object/blob with the entire contents of the file? Or does it store it in a more space-efficient manner?

Re: Some Git internals

#7

Post by shadykiller » Fri, Dec 25, 2020, 10:41 PM UTC

Git is really simple at the core and fun to poke around with. I gave a talk in RubyConf India about poking with git internals using ruby.

It was fun. Link for anyone interested(not very high quality but watchable):

https://www.youtube.com/watch?v=lPlwkxrG2NM

Re: Some Git internals

#8

Post by glandium » Fri, Dec 25, 2020, 10:48 PM UTC

ufo wrote: post #6

A dumb question: if I make a commit changing just a single line in a large file, does this create a completely new object/blob with the entire contents of the file? Or does it store it in a more space-efficient manner?

The former, until you run git gc, in which case the latter happens.

Re: Some Git internals

#9

Post by strogonoff » Fri, Dec 25, 2020, 11:00 PM UTC

Nice walkthrough! I did not know about FETCH_HEAD.

Another (complementing) way of getting an idea how Git works is by reading the source of Isomorphic Git[0]. Being in JS and with fewer (as of now) features, it’s a bit more accessible than reference Git.

[0] E.g. https://github.com/isomorphic-git/isomorphic-git/blob/main/s...

Re: Some Git internals

#10

Post by ufo » Fri, Dec 25, 2020, 11:15 PM UTC

glandium wrote: post #8

ufo wrote: post #6

A dumb question: if I make a commit changing just a single line in a large file, does this create a completely new object/blob with the entire contents of the file? Or does it store it in a more space-efficient manner?

The former, until you run git gc, in which case the latter happens.

Wow! Running git gc just shrunk my .git folder from 18MB to only 3MB.